A polyvinyl chloride film has represented as sheets for forming and has been preferably used from a view point of workability. However, since this film has problems such as toxic gas generation when it burns, bleeding-out of plasticizer and the like, novel material having reduced environmental burden is demanded in light of recent requirements for environmental protection.
In order to satisfy the aforementioned requirements, non oriented sheets comprised of polyester, polycarbonate and acrylic resins, which are not chloride-containing materials, are used in a wide field. Specially, a non oriented sheets comprised of a polyester resin is considerable because it has high physical properties and transparency, and is economically excellent. For example, JP 9-156267A, JP 2001-71669A, JP 2001-80251A, JP 2001-129951A and JP 2002-249652A disclose non oriented polyester sheets comprised of substantially amorphous polyester resins in which about 30% of ethylene glycol units in polyethylene terephthalate are substituted with 1,4-cyclohexanedimethanol.
Although the above non oriented polyester sheets satisfy formability and lamination properties, they have neither sufficient heat resistance nor solvent resistance due to non orientation. Thus, they have not satisfied the high demand in a commercial market.
JP 9-187903A, JP 10-296937A, JP 11-10816A and JP 11-268215A disclose processes for solving the above problems by using biaxially oriented polyethylene terephthalate films.
However, according to the above processes, heat resistance and solvent resistance are improved, but formability becomes insufficient. Thus, they have not satisfied the demand in a commercial market in total balance of quality.
JP 2001-347565A discloses a process for solving the above problem by specifying the stress at 100% elongation of films.
According to this process, formability is improved with respect to other processes, but its level has not been sufficient to satisfy the high demand on formability in a commercial market. Especially, there remain problems in formability which conforms lowering of forming temperature and in finish of products.
The present inventors have made efforts to solve the aforementioned problems and have already proposed a process for solving the above problems by using copolyester resin with a specified formulation as a raw material and specifying the stress at 100% elongation of the films in Japan Patent Application No. 2002-233694 and Japan Patent Application No. 2003-309894.
According to the above processes, in molding, since the forming pressure is high, formability which conforms lowering of forming temperature and finish of products can be greatly improved, satisfying the demand of a commercial market. However, in forming processes for which a commercial need recently becomes stronger, such as pressure forming and vacuum forming, further improvement in finish of products.